1. John Dalton (1766–1844) Ernest Rutherford (1871 – 1938) J. J. Thomson (1856 – 1940)

2. UEQ: How does the structure of matter influence its physical and chemical behavior?

3.  Atom  Electron cloud  Isotope  Nucleus  Proton  Neutron  Electron  Mass number  Atomic number  Average atomic mass

4. History of the Atom Democritus (400 BC) proposed idea that all matter is made up of atoms

5. History of the Atom Aristotle disagreed and said that matter was uniform throughout and not composed of smaller particles.

6. History of the Atom Dalton (1800’s) proved atoms did exist BUT he thought the atom was a solid sphere

7. History of the Atom Thomson (1904) proposed electrons were dispersed throughout a positively charged sphere (“plum- pudding”)

8. History of the Atom Rutherford (1911) disproved Thomson’s model by using the gold foil method. This proved that there was a dense, positive center surrounded by electrons.

9. History of the Atom Bohr (1913) hypothesized electron travel around fixed orbits around the nucleus Chadwick concluded the nucleus was made of protons and neutrons

10. History of the Atom Electron Cloud model (current) Electrons do not follow fixed orbit; but, tend to be at certain areas around nucleus at any given time

11.  Structure of the atom  3 subatomic particles identify the element  1. protons  Ernest Rutherford (1909)  (+) charge  Relative mass 1.007 276– or ~1 amu  Mass of element  Made of 3 quarks  In nucleus, held by nuclear forces  Identifies the element

12.  2. Neutron (N)  James Chadwick (1932)  No charge; neutral  Relative mass = 1.008 665 – or ~1 amu  In nucleus and held by nuclear forces  isotopes- atoms of same element with different #’s of neutrons  Contributes to mass of atom  Made of 3 quarks

13.  3. Electron (e-)  J.J. Thomson (1897)  ( – ) charge  Relative mass 0.000 5486  In orbitals, within the electron cloud  Makes volume of atom (100,000 times larger than diameter of nucleus)  Valence electrons - # in last energy level determines the chemical activity

14.  Atomic Number  Number of protons  Can also tell you number of electrons  Atomic Mass  Number of protons and neutrons of an atom

15.  Average Atomic Mass  Weighted average mass of the mixture of an element’s isotopes Example: We have a box of 2 types of marbles (100 total). If 25% of these marbles have a mass of 2 g and 75% have a mass of 3 g, then what is the average mass of the marbles?

16.  Mathematical Formulas  # of neutrons = mass # - atomic #  Mass Number = neutrons + protons  Atomic # = mass # - # of neutrons

17. Nuclear Symbol superscript subscript Hyphen notation  Element (name or symbol) hyphen mass #

18.  Isotope  Elements of same atomic number with different number of neutrons

19.  Common Isotopes and Uses  Hydrogen 1,2 Tracers for metabolic studies  Oxygen 16 Metabolic studies and determining temperature of ancient seas  Carbon 12 Metabolic studies and dating recent archeological artifacts  Phosphorus 31 Metabolic and ecological tracers, studies of nucleotides and nucleic acids  Sulfur 32, 33, 34 Labeling Proteins  Cobalt 59 Cancer therapy, source of gamma rays